1. Field of the Invention
The present invention relates to carbon dioxide (CO2) compression and storage for CO2 emission reduction purposes in mobile applications or in applications where an energy production cycle is used to produce work and where CO2 compression is required.
2. Description of the Prior Art
The currently accepted thinking is that global warming is due to emissions of greenhouse gases such as CO2 and methane (CH4). About a quarter of global CO2 emissions are currently estimated to come from mobile sources, i.e., automobiles, trucks, buses and trains that are powered by internal combustion engines (ICEs). This proportional contribution is likely to grow rapidly in the foreseeable future with the projected surge in automobile and truck ownership in developing countries. Accordingly, controlling CO2 emissions is very important.
Carbon dioxide management from mobile sources presents many challenges including space and weight limitations, the lack of any economies of scale and the dynamic nature of the operation of the ICEs powering the mobile sources.
Prior art methods for the capture of CO2 from combustion gases have principally focused on stationary sources, such as power plants. Those that address the problem of reducing CO2 emissions from mobile sources employ combustion using oxygen and provide no means for the regeneration and reuse of the CO2 capture agent, and/or make no use of waste heat recovered from a heat source. Combustion using only oxygen requires an oxygen-nitrogen separation step which is more energy-intensive than separating CO2 from the nitrogen-containing exhaust gases resulting from the use of atmospheric air and the separation problem would be made even more difficult if attempted on board the vehicle.
The focus of CO2 capture technology has been on stationary or fixed sources. The capture of CO2 from mobile sources has generally been considered too expensive, since it involves a distributed system with a reverse economy of scale. The prior solution to the problem has appeared to be impractical due to on-board vehicle space limitations, the additional energy and apparatus requirements, and the dynamic nature of the vehicle's operating cycle, e.g., intermittent periods of rapid acceleration and deceleration.
Methods, systems, and apparatus that address the problems of efficiently and cost-effectively reducing the CO2 emissions from mobile sources, e.g., vehicles powered by internal combustion engines, by the capture and temporary on-board storage of the CO2 from the engine's exhaust gas stream are still in their infancy.
As used herein, the term “internal combustion engine”, or ICE, includes heat engines in which a hydrocarbon-containing fuel, typically a conventional liquid hydrocarbon fuel, is burned to produce power or work and generates waste heat that must be removed or dissipated.
As used herein, the term “mobile source” means any of the wide variety of known conveyances that can be used to transport goods and/or people that are powered by one or more internal combustion engines that produce an exhaust gas stream containing CO2. This includes all types of motor vehicles that travel on land, airplanes and ships where the exhaust gas from the ICE is discharged into a containing conduit before it is discharged into the atmosphere.
As used herein, the term “waste heat” is the heat that a typical ICE produces that is contained principally in the hot exhaust gases (˜300° C. to 650° C.) and the hot coolant (˜90° C. to 120° C.). Additional heat is emitted and lost by convection and radiation from the engine block and its associated components, including heat transfer fins and surfaces of air-cooled engines, and the components through which the exhaust gas passes, including the manifold, pipes, catalytic converter and muffler. This heat energy totals about 60% of the energy that typical hydrocarbon (HC) fuels produce when combusted.
The term “vehicle” as used herein is to be understood as a convenient shorthand and synonymous with “mobile source” and is coexistensive with “conveyances”, generally, as that term is used above.
The methods and systems for on-board treatment of an exhaust stream containing CO2 emitted by a hydrocarbon-fueled ICE used to power a vehicle in order to reduce the amount of CO2 discharged into the atmosphere, include, among others, a process of CO2 densification, which involves reducing the temperature and volume of the CO2 to at least a liquefied state. Densification includes separation of substantially pure CO2 from the engine exhaust gases and temporary storage of the densified CO2 on board the vehicle for later use in any of a wide variety of known commercial and industrial uses, or for transfer to a permanent storage site.
An important part of any apparatus and method used for CO2 recovery is the use of a CO2 compressor that requires mechanical energy for its operation. However, providing the mechanical energy for operating or driving the compressor is accompanied by the problems associated with providing auxiliary power to meet the requirements of operating the CO2 compressor.
Accordingly, a problem addressed by the present invention is how to meet the objective of minimizing energy burdens imposed on the ICE or by the consumption of additional fuel for driving a CO2 compressor associated with an on-board CO2 capture system for removing CO2 from the exhaust gas stream produced by the ICE that powers the mobile source.